1. Field of the Invention
The present invention generally relates to position detecting apparatus and, more particularly, is directed to a position detecting apparatus utilizing magnetic reluctance elements to detect a position or the like of a magnetized scale such as a magnetized rotor or a magnetized scale or the like.
2. Description of the Prior Art
It is known that a detected signal from a position detecting apparatus having a magnetic reluctance element contains a harmonic component other than a fundamental wave component. To remove such harmonic component, it is proposed to provide a constant clearance between the magnetic scale and the position detecting apparatus. According to this proposal, the harmonic component cannot be removed sufficiently. Also, mechanical position accuracy of the apparatus must be increased in order to set the constant clearance between the magnetic scale and the position detecting apparatus and the constant clearance cannot be set without difficulty.
According to the prior art, a pattern layout of the magnetic reluctance element lines is set so as to make the length of the magnetic reluctance line substantially equal to the wavelength of the harmonic component, thereby a detected signal considerably approximated to a sine wave, which is the fundamental wave, being produced from the position detecting apparatus.
FIGS. 1A, 1B, FIG. 2 and FIGS. 3A, 3B illustrate examples of position detecting apparatus according to the prior art, respectively.
FIG. 1A shows a magnetized scale 1, and as shown in FIG. 1A, the magnetized scale 1 is formed by sequentially providing a plurality of magnets 3 at a lattice pitch .lambda. to form lattices 2, 2. FIG. 1B shows a magnetic sensor 4 having a predetermined magnetic reluctance element pattern, that is, a strip-shaped pattern. In the magnetic sensor 4, magnetic reluctance elements A1, A2, . . . A4 and magnetic reluctance elements B1, B2, . . . B4 are respectively aligned with an interval of .lambda./4 therebetween magnetic reluctance element members A1a, A2a, . . . A4a and magnetic reluctance element members A1b, A2b, . . . A4b forming the magnetic reluctance elements A1, A2, . . . A4 are aligned with an interval of .lambda./6 therebetween. Also, a magnetic reluctance element members B1a, B2a, . . . B4a and a magnetic reluctance element members B1b, B2b, . . . B4b forming the magnetic reluctance elements B1, B2, . . . B4 are aligned with an interval of .lambda./6.
If a voltage is applied to the thus arranged magnetic sensor 4 in the polarities (+) and (-) shown in FIG. 2 and if differential amplifiers (not shown) are respectively connected to output terminals A, A' and B, B', then the differential amplifiers derive detected signals of phases A and B. In that case, since the magnetic reluctance elements having the pitch .lambda./6 and the magnetic reluctance elements having the pitch (n+1/2).lambda. are formed in the magnetic sensor 4, the magnetic sensor 4 derives detected signals from which an even-numbered order harmonic component and a ternary harmonic component are removed.
FIG. 3A shows the same magnetized scale 1 as that of FIG. 1A. FIG. 3B shows a magnetic sensor 5 having other predetermined magnetic reluctance element pattern, that is, a so-called folded pattern. In this magnetic sensor 5, two folded patterns 6, each being formed in 19.lambda./3, are formed in the longitudinal direction of the magnetized scale 1 with an interval of 22.lambda./24 therebetween. A dotted portion shown in FIG. 3 illustrates a conductor portion 7 formed by a thin film forming technique.
When the voltage is applied to the thus constructed magnetic sensor 5 in the polarities of (+) and (-) of FIG. 3B, output signals expressed by the following equations (1) and (2) are developed at output terminals E and G so that even-numbered order harmonic component and the ternary harmonic component can be removed from the detected signals. In the following equations (1) and (2), a distortion component is removed in order to more clearly understand the principle of this magnetic sensor 5. EQU SIN.theta.+SIN (.theta.+60) (1) EQU COS.theta.+COS (.theta.+60) (2)
In this way, the even-numbered order harmonic component and the ternary harmonic component can be removed from the detected signals. In this case, if the folded pattern is modified, then odd-numbered order harmonic components exceeding the ternary harmonic component can be removed from the detected signals as will be described later.
In the position detecting apparatus having the magnetic sensors 4 and 5 shown in FIGS. 1B and 3B, however, if the magnetic scale to be detected thereby is a magnetized rotor 8 provided as a rotary encoder and which is rotated in the direction shown by an arrow AW in FIG. 4, then a clearance S1 between the central portion of the magnetic sensor 4 or 5 in the tangential direction of the circumferential portion of the magnetized rotor 8 and the rotor 8 and a clearance S2 between the end portion of the sensor 4 or 5 and the rotor 8 become different from each other. As a consequence, the amplitude of the detected signal is fluctuated so that, in actual practice, this magnetic sensor cannot be utilized as the position detecting apparatus.
Further, even though the magnetic scale is the magnetized scale 1 provided as the linear encoder, the length of the magnetized scale 1 with the slit-like pattern and the folded pattern in its length direction is relatively increased so that clearances S3 and S4 between respective ends of the magnetic sensor 4 or 5 and the scale 1 in the longitudinal direction of the magnetized scale 1 become different in value. Also in this case, the amplitude of the detected signal is fluctuated. Accordingly, in order to remove the above disadvantages, the mechanical position accuracy of the position detecting apparatus must be increased.
Furthermore, in the slit-shaped pattern shown in FIG. 1B, the magnetic reluctance element members A1b to A4b and the magnetic reluctance element members B1b to B4b must be aligned in parallel to the magnetic reluctance element members A1a to A4a and the magnetic reluctance element members B1a to B4a with a phase displacement of .lambda./6 in order to cancel the ternary harmonic component so that, when the lattice pitch .lambda. of the magnetized scale 1 is reduced, then the space of the phase displacement of .lambda./6 also is reduced, causing mutual interference between the adjacent magnetic reluctance element members, which produces a new harmonic component distortion in the detected signal. Moreover, when the lattice pitch .lambda. is further reduced, the magnetic reluctance element members A1b to A4b and the magnetic reluctance element members B1b to B4b which are displaced in phase by .lambda./6 cannot be inserted into the pattern from a physics standpoint. Similarly, the magnetic reluctance element patterns displaced in phase by .lambda. /10 cannot be newly inserted into the magnetic sensor in order to cancel a quinary harmonic component.
On the other hand, in the folded pattern shown in FIG. 3B, if the clearances of the adjacent folded patterns 6 relative to the magnetized scale 1 are different as described with reference to FIG. 5, then an amplitude difference occurs between the detected signals, which causes a measurement error. For this reason, it is preferable that the folded pattern can be suppressed from being extended in the longitudinal direction of the magnetized scale 1 as much as possible. However, when a quinary harmonic component is removed in addition, for example, to the removal of the ternary harmonic component, a new folded pattern must be provided additionally, which unavoidably makes the distance between the folded patterns longer.